The present invention relates to a method for automatically cutting pieces from a patterned fabric.
Fields of application for the invention are in particular the clothing industry and the furniture industry.
When making articles of clothing or pieces of furniture involving assembling together pieces cut from a fabric, there are special constraints if the fabric is patterned, the term "patterned fabric" designating herein any flexible sheet textile material printed with a pattern that is repeated with a uniform pitch. The pitch of the fabric, or pattern repeat pitch, is the distance between successive repeating patterns.
It is then desirable or even necessary to ensure that the pattern continues uninterrupted between two assembled-together pieces, e.g. two pieces of a garment sewn together, or two pieces intended to be adjacent, e.g. two portions of a garment situated side-by-side while the garment is being worn, or two cushions of a sofa placed side-by-side.
In order to satisfy these constraints, it is known that the pieces can be associated with absolute or relative position references, and a hierarchy can be established between main pieces and secondary pieces.
An absolute position reference is normally associated with a main piece. It characterizes the absolute positioning of the main piece relative to the pattern of the fabric. The position of a piece relative to the pattern is characterized by the fact that a given point on the surface of the piece occupies a determined relative position relative to the patterns surrounding it. Thus, pieces whose locations on the surface of the fabric can be deduced from one another by translations through an integer number of pattern pitch steps occupy the same positions relative to the pattern.
Relative position references are associated with two pieces that are to be assembled together, while taking into account constraints related to the existence of the pattern. They identify the locations of two match points that are to be brought in register with each other on assembling together the pieces.
For example, for a jacket, a front piece may constitute a main piece. An absolute position reference may optionally be associated with the front piece, e.g. when it is desired for a complete pattern to be visible at a particular location of the piece. The sleeve, the collar, and the pocket flap then constitute secondary pieces. For each of these secondary pieces, a match point is determined so as to correspond to the location of the associated match point on the main piece.
Naturally, match points may be defined not only between a main piece and a secondary piece, but also between two secondary pieces, one of them then acting as main piece relative to the other.
It is also known that fabric can be cut automatically. Automatic cutting installations have been sold by the Applicant for many years.
An automatic cutting method includes a layout-definition operation which consists in optimally determining the positions of the pieces to be cut from a strip of fabric. The layout is chosen so as to minimize fabric wastage while satisfying certain constraints: (cutting on or off the grain, minimum spacing between pieces to be cut, etc.). With a patterned fabric, there are also constraints related to complying with the locations of absolute position references and of relative position references. Systems enabling an operator to define layouts by means of computer workstations and of specialized software are known, including systems that can be used for patterned fabrics.
To perform cutting, the fabric is spread out on a cutting table in one or more superposed layers which may be held by suction via the table. Cutting is performed by means of a tool carried by a head which is displaced relative to the cutting table as a function of the predetermined layout. Cutting may be performed by a vibrating blade, a laser, a water jet, etc.
Particular difficulties appear when the fabric is a patterned fabric.
A first problem to be solved, if a plurality of superposed layers of patterned fabric are to be cut simultaneously is that a lay-up of layers must be formed so that the patterns are exactly superposed. A known technique consists in using needles which pass through the lay-up and prevent the layers from slipping relative to one another. Reference may be made to Document FR-A-2 644 484.
A second problem which arises in practice is the problem of the reference fabric used to define the layout not coinciding with the fabric actually spread out on the cutting table. This gives rise in particular to the following: on the cutting table, by going to the co-ordinates of a reference point of a piece in the layout, it can be observed that the corresponding point on the spread-out fabric does not always occupy the desired relative position relative to the pattern on the real fabric. These shifts are of varying size and, in practice, they are inevitable. They are caused by printing errors and/or by deformation of the fabric that can result in the pattern repeat pitch being non-uniform. As a result, the pre-established or ideal layout must be modified so as to correspond to the reality of the fabric as spread out.
One method for performing such layout modification automatically or semi-automatically is described in Document U.S. Pat. No. 4,853,866. After the patterned fabric has been spread out on the cutting table, a camera is brought to the various locations corresponding to the coordinates of the reference points. The real image of the fabric in the vicinity of the assumed location of an absolute position reference point is compared with the ideal image that the vicinity should have, the comparison being performed by digitizing the real image and correlating it with a recorded ideal image. Furthermore, the real images of the fabric in the vicinities of the match points are taken and stored so as to compare the real images of the vicinities of two corresponding match points. The results of the comparisons are used to offset the positions of the pieces in the layout so as to obtain a modified layout which corresponds to the reality of the spread-out fabric and in compliance with which the spread-out fabric is then cut.
That known method suffers from several drawbacks which affect the productivity of the installation and substantially increase the cost of the installation. Fully exploring all of the locations corresponding to the stored co-ordinates of the reference points requires a non-negligible amount of time during which the cutting installation is not available. In addition, such full exploration involves storing images, which requires large digital storage means, it being necessary to store the image of the vicinity of a match point on a piece so long as the image of the corresponding match point on another piece has not been detected and digitized, and so long as the two images have not been compared. Furthermore, full exploration requires a cutting table that is long enough for the length of fabric corresponding to an entire layout to be spread out thereon, which means that that known method cannot be implemented in installations using short cutting tables for cutting fabric that is plain or that does not require matching.
It has also been proposed, in Document WO-A-91/17029 to insert into the layout reference pieces of repetitive shape at constant intervals equal to an integer number of ideal pattern repeat pitch steps of the pattern of the fabric. By examining the locations of the pieces on the spread-out fabric, it is possible to verify whether an offset exists between the ideal repeat pitch and the real repeat pitch of the pattern of the fabric, and to correct the layout where necessary. This examination may be made by cutting out reference pieces or by visually examining their locations on the spread-out fabric. The method disclosed in Document WO-A-91/17029 therefore makes it necessary to interrupt cutting out each time a new reference piece is encountered, which penalizes efficiency considerably, in particular since the spacing between reference pieces must not be too large so that it is possible for any offset occurring between the ideal repeat pitch and the real repeat pitch of the pattern to be corrected sufficiently rapidly. Furthermore, the presence of reference pieces in the layout complicates the layout and gives rise to inevitable wastage of material.